Re: xhci power to external device

[Michael van Elst <mlelstv%serpens.de@localhost>]

On Tue, Feb 19, 2019 at 11:30:22AM -0500, Greg Troxel wrote:
> > That information is mostly used to calculate the power budget, If
> > it would be exceeded, the device isn't allowed to draw more power.
> How common is it for USB controllers to actually do this calculation and
> selectively enable, vs being built to supply 500/900 per port?
> Looking at NetBSD drivers quickly, I don't see this.

usb_subr.c:707ff


> Certainly current limiting on power supplies is normal.

Probably. Hubs notice when the current limit is exceeded, I don't see
that our controllers could set a current limit but there is probably
some fuse or other current limiter to prevent damage.


Greetings,
-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."